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IEEE Conference on Global Communications (GLOBECOM)

作者： Jiaojie Wang Fei Wang Xi Zhang Yuanyuan Yang College of Electronic and Information Engineering Southwest University China Department of Electrical and Computer Engineering Networking and Information Systems Laboratory Texas A&M University College Station TX USA Department of Electrical and Computer Engineering Stony Brook University Stony Brook NY USA

ISBN: (数字)9798350351255

ISBN: (纸本)9798350351262

Intelligent reflecting surface (IRS) has been widely recognized as one of the key techniques to improve secure communications performances. However, most existing works mainly focus on the passive beamforming, i.e., phase-shifts, design of a single IRS, without taking into account the cooperations among multiple IRSs and the optimizations of their relative positions. To overcome these deficiencies, in this paper we propose the joint optimizations between the transmit beamforming of massive multiple-input multiple-output (massive-MIMO) access point (AP) and double-IRS’ positions and passive beamforming over 6G secure mobile networks. In our proposed networking architectures, AP transmits data to multiple mobile users (MUs) through reflections of two cooperative IRSs under the existence of one eavesdropper (Eve). First, we formulate a secrecy rate optimization problem to maximize the expectations of all MUs’ aggregate secrecy rates when Eve’s exact position is unknown. Second, leveraging the deep reinforcement learning (DRL), we develop two joint deploying and beamforming schemes to tackle the uncertainty of Eve’s exact position. Finally, we validate and evaluate our developed schemes by conducting the extensive simulations, showing the significant performances improvements of our developed schemes through jointly optimizing IRSs’ positions/orientations and transmit-beamforming of massive-MIMOAP as the function of the predicted Eve’s deploying areas.

关键词： 6G mobile communication Uncertainty Array signal processing Wireless networks Predictive models Deep reinforcement learning Reflection MIMO Global communication Optimization

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A Comparative Study on Partial Discharge and Dielectric Strength of MMEI Flat Samples under AC and DC Conditions at Atmospheric Pressure

A Comparative Study on Partial Discharge and Dielectric Stre...

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IEEE Green Energy and systems Conference (IGESC)

作者： Saikat Chowdhury Anoy Saha Md Asifur Rahman Mona Ghassemi Department of Electrical and Computer Engineering Zero Emission Realization of Optimized Energy Systems (ZEROES) Laboratory The University of Texas at Dallas Richardson TX USA

ISBN: (数字)9798350379617

ISBN: (纸本)9798350379624

The shift towards electrifying transportation systems has become a pivotal strategy in achieving net-zero emissions, driving extensive adoption across the transportation sector. Consequently, the aviation industry is transitioning to all-electric aircraft (AEA). For AEA, an electric power system (EPS) that delivers high power while maintaining low system mass is crucial. Cables are vital components in this future EPS, and one way to reduce their weight is by operating at higher voltages. However, designing insulation systems for higher voltages poses challenges due to increased partial discharge (PD) activity in harsh aviation environments characterized by extremely low pressures and moisture levels. To address these challenges, multilayer multifunction electrical insulation (MMEI) systems have been developed, offering higher breakdown strength compared to single-layer insulation systems. Our previous study proposed some novel MMEI designs for medium voltage direct current (MVDC) power cables capable of operating at low pressures. In this paper, the PD characteristics of these designed MMEI systems are analyzed using the OMICRON MPD 800 under both AC and DC conditions on flat samples. Additionally, the dielectric strength for AC and DC is tested and compared using the Weibull distribution method.

关键词： Partial discharges Insulation Breakdown voltage Transportation Power system stability Discharges (electric) Weibull distribution Aircraft Stress Standards

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Characterizing Nonlinear Field Dependent Conductivity Layers to Mitigate Electric Field Within (U)WBG Power Modules Under High Frequency, High Slew Rate Square Voltage Pulses

Characterizing Nonlinear Field Dependent Conductivity Layers...

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IEEE Texas Power and Energy Conference (TPEC)

作者： Pujan Adhikari Mona Ghassemi Department of Electrical and Computer Engineering Zero Emission Realization of Optimized Energy Systems (ZEROES) Laboratory The University of Texas at Dallas Richardson TX USA

A vast majority of research on (U)WBG power modules has been going on to implement nonlinear resistive field grading material on metal-brazed substrates in reducing the electric field that is maximum at triple points (TPs). However, nearly all investigations have been conducted under either DC or 50/60 $\mathbf{H}_{\mathbf{Z}}$ sinusoidal AC voltages, even though the actual operation of envisioned (U)WBG power modules involves high-frequency square voltages with high slew rates. It has been validated by several studies that fast rise times of square voltages rapidly degrade the breakdown strength of insulation materials, leading to premature failure. Therefore, this paper introduces a nonlinear resistive field grading material or field-dependent conductivity (FDC) layer around the TP and metal edges to evaluate the electric field mitigation under a high frequency and high slew rate square voltage. The modeling and simulation of both coated and uncoated (U)WBG substrates were performed in COMSOL Multiphysics to assess the electric field reduction with the nonlinear FDC layer. The improvement of reduction in electric field under 100 kHz high slew rate square voltage is compared with that of 60 Hz. The results reveal a significant decrease in field stress at the TP, even under square voltages with fast rise times and high frequencies, when applying a nonlinear FDC coating, as opposed to the uncoated substrate. The influence of switching field $(\mathbf{E}_{\mathbf{b}})$ and nonlinearity coefficient $(\alpha)$ of nonlinear FDC layer is studied under 100 kHz square voltage, and it is concluded that $\alpha$ and $\mathbf{E}_{\mathbf{b}}$ should be more than 10 and less than 8 kV/mm, respectively to achieve effective performance of resistive field grading material.

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A Review of Insulation Challenges and Mitigation Strategies in (U)WBG Power Modules Packaging

A Review of Insulation Challenges and Mitigation Strategies ...

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IEEE Texas Power and Energy Conference (TPEC)

In the ever-growing landscape of electrical power demand, the future of power electronics module packaging lies in the realm of wide-bandgap (WBG) materials, including silicon carbide (SiC), gallium nitride (GaN), and cutting-edge ultra WBG (UWBG) materials like diamond, aluminum nitride (AlN), and hexagonal-boron nitride (h-BN). These materials offer superior properties to traditional silicon-based devices, promising higher power density, reduced weight, and increased operating temperature, voltage, and frequency. However, pushing the boundaries for power electronics modules presents challenges in insulation systems as the encapsulation material and the ceramic substrate may not withstand the functional parameters, potentially leading to unfavorable conditions like high field stress and partial discharge (PD), ultimately resulting in insulation failure. This paper presents a thorough analysis of the characteristics of the electrical insulation materials used in power electronics devices based on the research in WBG packaging conducted in recent years. The significance of maximum electric field stress at triple points (TPs) is examined. Furthermore, the paper reviews the strategies and techniques employed to mitigate the challenges related to maximum field stress and PDs in both encapsulation and substrate materials. It is concluded that the mitigation strategies are promising in improving insulation systems for packaging, but the studies lack their implementation under actual operating conditions of WBG power modules.

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MVDC Bipolar Power Cables with Rectangular Geometry design for Envisaged All-Electric Wide-Body Aircraft

MVDC Bipolar Power Cables with Rectangular Geometry Design f...

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IEEE Texas Power and Energy Conference (TPEC)

作者： Anoy Saha Mona Ghassemi Department of Electrical and Computer Engineering Zero Emission Realization of Optimized Energy Systems (ZEROES) Laboratory The University of Texas at Dallas Richardson TX USA

designing power cables that provide high power and low system mass is one of the major goals in achieving the future all-electric wide-body aircraft. Radiative and convective heat transfers from a cable's surface to the surrounding air determine how much current is permitted to flow through it. At a cruising altitude of 12.2 km (18.8 kPa) for wide-body aircraft, the limited heat transfer by convection poses thermal issues for the design of aircraft cables. These thermal challenges are exacerbated for bipolar electric power systems (EPS), which are usually made up of two power lines next to each other. The cable's surface area affects both convective and radiative heat transfers. Changing the shape of the cable is one technique to improve heat transfers and compensate for the reduced convective heat transfer caused by low air pressure. In comparison to cylindrical and cuboid cables, the rectangular geometry design gives a bigger contact area with the surrounding atmosphere for the same cross-section area, hence it is anticipated that the heat transfer would rise and as a result, the cable's maximum power-carrying capability will be higher. The purpose of this paper is to design ±5 kV bipolar MVDC power cables with rectangular geometry to raise the maximum current carrying capacity of the cable and analyze its performance with bipolar cylindrical and cuboid geometries.

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A Test System Meeting Requirements Under Normal and Contingency Conditions at Multiple Loadings for Transmission Expansion Planning

A Test System Meeting Requirements Under Normal and Continge...

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Proceedings of the IEEE Dallas Circuits and systems Workshop (DCAS)

作者： Bhuban Dhamala Mona Ghassemi Department of Electrical and Computer Engineering Zero Emission Realization of Optimized Energy Systems (ZEROES) Laboratory The University of Texas at Dallas Richardson TX USA

ISBN: (数字)9798350349535

ISBN: (纸本)9798350349542

This paper introduces a high-voltage test system tailored specifically for transmission expansion planning (TEP). The network incorporates long transmission lines, and the line series impedance and shunt admittance for each line are computed utilizing the equivalent $\pi$ circuit model for long transmission lines to account for the distributed nature of line parameters. The proposed test system offers technically feasible load flow solutions under normal and all single contingency conditions for three distinct loading scenarios: peak, dominant, and light loading conditions. As the real power system is subject to various loading scenarios and should be effectively operable under all conditions, this test system accurately replicates the properties of real power systems. The test system introduced in this paper can be a valuable resource for TEP research.

关键词： Technical requirements Power transmission lines Loading Contingency management High-voltage techniques Planning Power system reliability

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Influence of Rise Time on the Aging of Electric Machine Windings

Influence of Rise Time on the Aging of Electric Machine Wind...

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Conference on electrical Insulation and Dielectric Phenomena, (CEIDP)

作者： Easir Arafat Md Asifur Rahman Farzana Islam Mona Ghassemi Department of Electrical and Computer Engineering Zero Emission Realization of Optimized Energy Systems (ZEROES) Laboratory The University of Texas at Dallas Richardson TX USA

ISBN: (数字)9798350366679

ISBN: (纸本)9798350366686

This study examines how fast rise times, which are common in modern power electronics and drive systems, affect the aging of electric machine windings. It focuses on how to ensure these windings can last longer and work reliably in electrical systems. A twisted pair magnet wire with insulation commonly used in wound machines was used to get experimental data to understand how different voltage waveforms can influence endurance testing of motor insulation systems powered by inverters. Unlike past studies that looked at comparatively slower rise times and fewer repetitions, this research specifically addresses the challenges posed by next-generation wide bandgap (WBG)-based conversion systems. These systems operate at very high speeds, up to 100 kV/μs, and switch frequencies up to 500 kHz, where both frequency and rise time are crucial factors affecting insulation aging over time.

关键词： Insulation Time-frequency analysis Electric machines Windings Voltage Switches Aging Reliability engineering Wire Testing

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When Graph Meets Retrieval Augmented Generation for Wireless Networks: A Tutorial and Case Study

arXiv

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arXiv 2024年

作者： Xiong, Yang Zhang, Ruichen Liu, Yinqiu Niyato, Dusit Xiong, Zehui Liang, Ying-Chang Mao, Shiwen Engineering Systems and Design Pillar Singapore University of Technology and Design Singapore College of Computing and Data Science Nanyang Technological University Singapore Computer Science and Design Pillar University of Technology and Design Singapore Chengdu611731 China Department of Electrical and Computer Engineering Auburn University AuburnAL36849 United States

The rapid development of next-generation networking technologies underscores their transformative role in revolutionizing modern communication systems, enabling faster, more reliable, and highly interconnected solutions. However, such development has also brought challenges to network optimizations. Thanks to the emergence of Large Language Models (LLMs) in recent years, tools including Retrieval Augmented Generation (RAG) have been developed and applied in various fields including networking, and have shown their effectiveness. Taking one step further, the integration of knowledge graphs into RAG frameworks further enhanced the performance of RAG in networking applications such as Intent-Driven Networks (IDNs) and spectrum knowledge maps by providing more contextually relevant responses through more accurate retrieval of related network information. This paper introduces the RAG framework that integrates knowledge graphs in its database and explores such framework’s application in networking. We begin by exploring RAG’s applications in networking and the limitations of conventional RAG and present the advantages that knowledge graphs’ structured knowledge representation brings to the retrieval and generation processes. Next, we propose a detailed GraphRAG-based framework for networking, including a step-by-step tutorial on its construction. Our evaluation through a case study on channel gain prediction demonstrates GraphRAG’s enhanced capability in generating accurate, contextually rich responses, surpassing traditional RAG models. Finally, we discuss key future directions for applying knowledge-graphs-empowered RAG frameworks in networking, including robust updates, mitigation of hallucination, and enhanced security measures for networking applications. © 2024, CC BY.

关键词： Knowledge graph

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Location of Shield Wires for Unconventional High Capacity Transmission Lines

Location of Shield Wires for Unconventional High Capacity Tr...

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Proceedings of the IEEE Dallas Circuits and systems Workshop (DCAS)

作者： Saikat Chowdhury Babak Porkar Mona Ghassemi Department of Electrical and Computer Engineering Zero Emission Realization of Optimized Energy Systems (ZEROES) Laboratory The University of Texas at Dallas Richardson TX USA

ISBN: (数字)9798350349535

ISBN: (纸本)9798350349542

To achieve net-zero emission in America by 2050, high voltage transmission capacity must expand ~60% by 2030 and triple by 2050 to connect further wind and solar facilities to demand. This expansion requires a capital investment in transmission capacity of $360 billion by 2030 and $2.4 trillion by 2050. Considering the high cost of building transmission lines, innovations toward high-capacity overhead lines have been targeted to reduce the number of transmission lines required. In our previous studies, we introduced unconventional high-capacity transmission lines. To realize these novel transmission lines, various aspects of line design should be studied, and this paper addresses determining the location and number of shield wires to protect these novel lines against lightning strikes. Lightning-induced overvoltage across line insulators is one of the key factors in power system outages. The design meets the shielding failure flashover rate (SFFOR) $\leq 0.05/100$ km-years for all three phases of the unconventional high-capacity transmission line. Brown-Whitehead equations were used to measure and analyze the striking distance for vertical strokes.

关键词： Technological innovation Power transmission lines Net zero Wires Lightning Flashover Transmission line measurements

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Effect of Forced Heat Convection on Heat Transfer for Bipolar MVDC Power Cables in Envisaged Wide-Body All-Electric Aircraft

Effect of Forced Heat Convection on Heat Transfer for Bipola...

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Proceedings of the IEEE Dallas Circuits and systems Workshop (DCAS)

作者： Md Asifur Rahman Anoy Saha Mona Ghassemi Department of Electrical and Computer Engineering Zero Emission Realization of Optimized Energy Systems (ZEROES) Laboratory The University of Texas at Dallas Richardson TX USA

ISBN: (数字)9798350349535

ISBN: (纸本)9798350349542

Since transportation is one of the primary sources of greenhouse gas (GHG) emissions, its electrification is essential for achieving the net-zero GHG emissions target. As a part of transportation electrification, all-electric aircraft (AEA) have emerged as a viable approach to achieve net-zero emissions in aviation. Electric power systems (EPS) with high power density and low system mass are required for future wide-body AEA. Power cables, as one of the key components of the aircraft EPS, must be constructed to maximize the overall power density of the EPS. Because of the limited heat transfer by convection at cruising altitudes of wide-body AEA, the design of power cables faces significant thermal challenges. These difficulties are worsened using bipolar MVDC EPSs, which are generally composed of two power cables, negative and positive poles, adjacent to one another. Heat transfers that occur through convection and radiation are influenced by the cable's surface area. To offset the decrease in convective heat transfer brought on by the low air pressure, one method is to apply forced heat convection. Increasing the velocity of forced air in a cable duct, either the surface temperature of the cable can be reduced, or the core diameter can be reduced along with the cable weight maintaining the same temperature obtained from natural heat convection. This paper examines the impact of forced heat convection on a conventional cylindrical bipolar cable system. The cable system is equipped with our novel designed ARC-SCT-MMEI insulation system delineated in the paper, and its performance is compared to that of natural heat convection.

关键词： Power system measurements Power cables Density measurement Net zero Ducts Power cable insulation Transportation

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